Final answer:
The nurse should start chest compressions with assisted manual ventilations. Bradycardia is an abnormally slow heart rate, and it is important to prioritize maintaining blood circulation and oxygenation. Reviewing possible underlying causes should also be done alongside immediate interventions.
Step-by-step explanation:
The nurse should start chest compressions with assisted manual ventilations for the 4-year-old child who has become unresponsive with a heart rate of 40 beats/minute, blood pressure of 88/70 mmHg, and oxygen saturation of 70. This child is experiencing a bradycardic event, which is an abnormally slow heart rate. Chest compressions with assisted manual ventilations can provide crucial circulation and oxygenation to the child's vital organs, including the brain, while waiting for further medical intervention.
Administering epinephrine via intraosseous (IO) or applying pads and preparing for transthoracic pacing may be potential interventions, but they are not the initial actions recommended in this situation. It is important to first prioritize basic life support measures, such as chest compressions, to maintain blood circulation and oxygenation.
Reviewing the possible underlying causes for bradycardia is also important, but it should be done alongside the immediate implementation of chest compressions and ventilations. Identifying and addressing the underlying cause can help guide further management and treatment decisions.